JiraService integration issue

Hi,
when trying to use gitlab native integration we get following error in our log files,

{
"severity":"ERROR",
"time":"2020-1202T15:20:44.791Z",
"correlation_id":"ANInjGZZXB7",
"service_class":"JiraService",
"project_id":323,
"project_path":"xxx/yyy",
"message": "Error sending message",
"client_url":"[https://<OUR_JIRA_URL>)](<OUR_JIRA_URL>)",
"error":"Not Found"
}

can you please help with some hints/references how to debug it further to understand the issue?

(option/settings are tested . also used “test integration” , everything seems ok)

Thanks,
Levon.